In the flotation separation of minerals, reagents containing a sulfoxy radical, such as sodium sulfite, sodium bisulfite and sodium metabisulfite (or alkali metal, alkaline earth metal or ammonium equivalents thereof), sulfur dioxide or other thionates are commonly used to improve the quality of the separation, particularly where sulfidic minerals such as chalcopyrite, pentlandite, pyrite, sphalerite, pyrrhotite or galena are present.
The sulfoxy radical-containing reagents act to depress certain minerals to allow an operator to selectively float the desired valuable sulfidic mineral.
There are, however, certain difficulties associated with the use of sulfoxy radical-containing reagents in flotation separation circuits. First, the cost of such reagents is quite high and it would prove beneficial if consumption thereof could be reduced or alternatively the quality or grade of the valuable concentrate could be increased using the same quantity of reagent.
Also, the effectiveness of the sulfoxy radical-containing reagent depends on a number of factors including pH, dissolved oxygen content of the slurry and the type of ore forming the slurry. For example, at relatively low concentrations of sodium sulfite, pyrite flotation is markedly slowed. This effect is increased at a higher pH level (by the addition of sodium hydroxide or lime). Depression of sphalerite by sodium sulfite has been previously reported, however, its effectiveness is not always clear. Sulfite addition does not appear to increase or decrease chalcopyrite flotation rates.
The effectiveness of the sulfoxy radical-containing reagent also depends upon conditioning times. Experience has shown that conditioning times have a marked effect on the flotation selectivity of certain ores. Also, the effectiveness of the sulfoxy radical-containing reagent depends upon the particle size of the minerals in the slurry. It has been found that finer sizes of sulfide minerals can be less sensitive to sulfoxy radical-containing reagent conditioning i.e. longer conditioning times may be required to depress certain minerals.
Of course, in addition to these difficulties, it is necessary for a plant operator to supply the selected sulfoxy radical-containing reagent to the plant site which is usually at a remote location. Transport, storage and preparation of the these reagents for use results in substantial additional costs.
Accordingly, it is an object of the present invention to overcome at least some of the disadvantages of the prior art or provide a commercial alternative thereto.